You may need to disable Secure Boot to run some PC graphics cards, hardware, or operating systems such as Linux or previous version of Windows.  While it is not a requirement on all PC or Notebooks, the systems that do need it disable will simply not boot from an external USB drive or even DVD.

Secure Boot helps to make sure that your PC boots using only firmware that is trusted by the manufacturer. You can disable Secure Boot through the PC’s firmware (BIOS) menus, but the way you disable it varies by PC manufacturer. If you are having trouble disabling Secure Boot after following the steps below, contact your manufacturer for help.

Disable Secure Boot

1. Before disabling Secure Boot, consider whether it is necessary. From time to time, your manufacturer may update the list of trusted hardware, drivers, and operating systems for your PC. To check for updates, go to Windows Update, or check your manufacturer's website.

2. Open the PC BIOS menu. You can often access this menu by pressing a key during the bootup sequence, such as F1, F2, F12, or Esc.

   Or, from Windows, hold the Shift key while selecting Restart. Go to Troubleshoot > Advanced Options: UEFI Firmware Settings.

3. Find the Secure Boot setting, and if possible, set it to Disabled. This option is usually in either the Security tab, the Boot tab, or the Authentication tab.

4. Save changes and exit. The PC reboots.

5. Install the graphics card, hardware, or operating system that’s not compatible with Secure Boot.

   In some cases, you may need to change other settings in the firmware, such as enabling a Compatibility Support Module (CSM) to support legacy BIOS operating systems. To use a CSM, you may also need to reformat the hard drive using the Master Boot Record (MBR) format, and then reinstall Windows.

Re-enable Secure Boot

1. Uninstall any graphics cards, hardware, or operating systems that aren’t compatible with Secure Boot.

2. Open the PC BIOS menu. You can often access this menu by pressing a key during the bootup sequence, such as F1, F2, F12, or Esc.

   Or, from Windows: go to Settings charm > Change PC settings > Update and Recovery > Recovery > Advanced Startup: Restart now. When the PC reboots, go to Troubleshoot > Advanced Options: UEFI Firmware Settings.

3. Find the Secure Boot setting, and if possible, set it to Enabled. This option is usually in either the Security tab, the Boot tab, or the Authentication tab.

   On some PCs, select Custom, and then load the Secure Boot keys that are built into the PC.

   If the PC does not allow you to enable Secure Boot, try resetting the BIOS back to the factory settings.

4. Save changes and exit. The PC reboots.

5. If the PC is not able to boot after enabling Secure Boot, go back into the BIOS menus, disable Secure Boot, and try to boot the PC again.

6. In some cases, you may need to refresh or Remove everything to its original state before you can turn on Secure Boot.